Establishing communication between bore holes in solution mining



Oct, 17, 1967 J. B. DAHMS ETAL 3,347,595

ESTABLISHING COMMUNICATION BETWEEN BORE HOLES IN SOLUTION MINING Filed May 3, 1965 E M SOLVENT PRODUCT MINERAL;

EFFLUENT CLAY INSOLUBLE BAND FIG. I

" INVENTORS EFFLUENT 5* a KINSOLUBLB BAND Bree/v P. same/v05 JAMES B. DAHMs m... GA 6 t4 fi lgNEYs FIG. 2

United States Patent 3,347,595 ESTABLISHING COMMUNICATION BETWEEN BORE HOLES IN SOLUTION MINING James Bowen Dahms, New Martinsville, W. Va., and Byron Priestly Edmonds, Pittsburgh, Pa., assignors to Pittsburgh Plate Glass Company, Pittsburgh, Pa., a corporation of Pennsylvania Filed May 3, 1965, Ser. No. 452,596 5 Claims. (Cl. 299-4) ABSTRACT OF THE DISCLOSURE Selected strata rich in product minerals are extracted from soluble deposits containing a plurality of strata of varying compositions. A flexible conduit is inserted through a cased bore hole communicating with the deposit in the vincinity of a thin insoluble band of insoluble materials. The flexible conduit is biased toward a second cased bore hole which also communicates with the deposit in the vicinity of the insoluble band. Extractant is forwarded down the flexible conduit to form a fluid travel path in communication with the spaced bore holes above the insoluble band.

This invention relates to solution mining a soluble. More particularly it is directed to establishing communication between pairs of bore holes penetrating a formation to the vicinity of a deposit of product minerals.

In a typical solution mining operation, one or more conduits are provided through a plurality of strata of varying composition to a lower deposit of product minerals. By product mineral is meant a mineral which it is commercially desirable to extract. These minerals are extractable with suitable solvents, typically with aqueous media including acids, steam, salt solutions, substantially pure water, etc. Bore holes fitted with suitable casings are typically provided as conduits. Additional conduits may be provided by passing tubes, pipes or hoses, for example, through the cased bore holes. Thus, a single bore hole may accommodate a plurality of conduits in the form of a centrally disposed tube with one or more annular passages between the tube and the casing of the bore hole.

The economics of a solution mining operation are often significantly improved when the product minerals are contacted with solvent over a substantial extraction surface. Many solubles, for example KCl-bearing minerals or trona, are slow to dissolve in the extracting solvents typically employed. Thus, an inordinate amount of time is required to establish a solution mining cavity sufficient- 1y large to provide the requisite extraction surface. Special techniques are required to provide a suitable extraction surface without first developing a substantial cavity by solution mining. One particularly advantageous method of solution mining is to establish a communicating passage or cavity between a plurality of bore holes which communicate with the vicinity of the product deposit at substantial distances from each other. By introducing solvent to one such bore hole (influent conduit) and withdrawing effluent through a remote conduit, solvent is caused to traverse a considerable distance. This spaced conduit system of solution mining offers many practical and economical advantages. The effective extraction sur-' face is large in such a system. In addition, the physically separated influent and eflluent streams are substantially out of direct heat transfer relationship. Insulation of the feed stream from the effluent stream is a significant advantage where the product mineral has a negative heat of solution such as, for example, KCl or trona.

Of primary importance in operating a multiple conduit solution mining system is rapidly establishing commethods while maintaining 3,347,595 Patented Oct. 17, 1967 munication between two or more conduits. One method of establishing such a communication is to simultaneously develop cavities adjacent the terminus of a plurality of conduits penetrating the formation. These cavities are usually developed by providing smaller diameter conduits inside the cased bore holes. Solvent is fed through the internally disposed conduits to extract soluble materials from the deposit. Enriched effluent is withdrawn through the spaces annular to the internal conduits thereby developing cavities in the formation. The cavities are then developed horizontally until they communicate to form a common passageway communicating with a plurality of concentric conduit placements. The internal tubes can then be removed and a multiple conduit system operated by feeding solvent to one or more cased bore holes and withdrawing effluent from one or more other cased bore holes.

An alternative method which has been employed with some success is to sink two bore holes through the earth to the vicinity of a product deposit. Pressure is then applied at the base of one or both of the bore holes to fracture the formation, thereby establishing a passageway communicating with both bore holes. This fracturing method of communication is difficult to control. It has been found that fractures may meander away from the desired direction of communication. Thus, where a plurality of bore holes has been sunk through a formation and communication between chosen bore holes is attempted by the fracturing technique, there is a substantial danger that the fracture will bring into communication bore holes which it is desired to maintain out of communication. In addition, it is difficult to maintain fractures in, for example, evaporite deposits. These deposits exhibit plastic behavior at the depths at which they are normally fractured. Thus, unless high hydraulic pressure is maintained at the fracture point, the fracture tends to close. A typical fracturing operation often requires the extended application of high pressures. Typical pressures, measured at the surface of the earth, range from about 0.8 to about 1.2 p.s.i. per foot of depth to the fracture in excess of normal hydrostatic pressure.

The present invention provides a rapid and economical method whereby communication is effected between two conduits within a time much reduced over the prior art good directional control. Thus, by the practice of thisinvention, a passageway is rapidly effected between two conduits without the attendant uncertainty of the prior art fracturing methods.

In the practice of this invention, a conduit, usually a cased bore hole, is provided through a subterranean formation to the vicinity of a product mineral deposit. Usually the product mineral deposit is situated between deposits of varying compositions and comprises several strata some of which are quite rich in product minerals interspersed with various soluble and insoluble materials.

Bands of insoluble minerals normally traverse the product deposit. Often these bands occur at the interface be tween a product deposit and a non-product stratum. These bands typically occur throughout the formation both above and below the product stratum. In the practice of this invention, the cased bore hole terminates above a band of insoluble minerals, preferably disposed beneath but near the product mineral deposit. If a suitable band is not present within an acceptable distance beneath the product deposit, it is sometimes advantageous to terminate the cased bore hole above a suitable band within the product minerals. The insoluble band is desirably in the proximity, for example, within about 250, preferably within about inches of the bottom of the product deposit.

A flexible conduit is passed through the cased bore hole insoluble band in the direction of a second conduit which fluent at the surface of the earth. In this fashion, a passageway is developed along the upper surface of the in-, soluble band in the direction of the second conduit. Of

course, the second conduit may also be a flexible conduit urged from. a second bore hole in the direction of the first named flexible conduit. In any event, communication is eventually established along the insoluble band between the two conduits.

After communication has been established, the flexible conduits internal to the bore holes can be removed. The cased bore holes are then utilized as influent and effluent conduits, respectively. Solvent is thus fed through the ink fluent conduit to extract soluble materials situated above the insoluble band. Enriched solvent is withdrawn from the efliuent casing. In this fashion the communicating passageway between the bore holes is developed and enlarged. The roof of the passageway is then gradually raised into the soluble product deposit. Thereafter, solution mining of the product mineral is effected in the usual manner.

The insoluble bands contemplated by this invention should be fairly rigid to resist dispersion by the solvent and abrasion by the flexible pipe as it is urged along the band., Thus, the band should be sufliciently resistant to serve as a pavement upon which the flexible conduit can be urged without penetrating the band. Suitable bands include calcium sulfate deposits, shale, slate and limestone strata or any similar band which is comprised primarily of insoluble consolidated material. Well consolidated clay bands of suitable thickness, for example, about 3 or more inches are employable. The band may be of any thickness sufiicient to provide the requisite. strength necessary to resist penetration by the conduit. A calcium sulfate band about 1 inch thick is usually satisfactory.

It is preferable to bias the conduit in the desired direction before it contacts the insoluble band. In this fashion,

an outside wall of the conduit rather than'the end of conduit contacts the insoluble band. The necessary bias can be provided by placing in the cased bore hole a biasing means such as an inclined plane or whipstock suitably located to urge the conduit in the desired direction.

The invention will be more readily understood with ref erence to the drawings of which FIG. 1 depicts a cased bore hole with a flexible conduit disposed therein; and

FIG. 2 depicts the same bore and flexible conduit during an :advancedstage of development in communication with a second conduit extending through a second cased bore hole.

Referring to the drawings, cased bore hole 1 is provided through a formation comprising a plurality of strata of soluble minerals and insoluble bands. A deposit of product minerals is disposed above an insoluble band. Disposed intermediate the product minerals and the insoluble band are additional strata of soluble minerals. Cased bore hole 1 terminates above the insoluble band, preferably in the product deposit. The insoluble band may be located within the product deposit or beneath the product. deposit as shown in'thedrawing. Near the bottom of casing 1 is disposed an orientation means 3 de-. picted as an inclined plane to bias flexible conduit 2 and impart a substantial horizontal component thereto.

It is desirable to attach to the end of flexible conduit 2 an orifice or nozzle 4. Solvent is fed through conduit 2 to the vicinity of the insoluble band. The solvent extracts soluble materials in the proximity of the band, and enriched solvent (effluent) is withdrawn from bore hole .1. The annular space between the bore hole casing and conduit 2 serves as the etfluent conduit. In this fashion a small cavity 8 is developed, preferably in contact with the upper surface of the insoluble band. As the flexible conduit is forced through bore hole 1, it eventually contacts the insoluble band or material bearing on the insoluble band. When the flexible conduit meets the resistance of the insoluble band, it tends to travel in the direction of bias as depicted in FIGURE 2.

At a distance remote from bore hole -1, a second bore hole 11 is provided through the formation to terminate above the insoluble band. The bore hole may terminate near the vicinity of the band to provide a target for cavity 8 as it is developed across the insoluble band.

Because the effluent casing or conduit should normally terminate near the bottom of the product mineral deposit in a producting solution mining operation, it is preferred to terminate bore hole 11 in the product deposit. A second conduit 12 is then provided through bore-hole 11 to extend closer to the insoluble band than does bore hole 11. As cavity 8 develops, it ultimately is brought into communication with conduit 12.

An immiscible non-solvent fluid such as a hydrocarbon oil is conveniently provided to cavity 8 along with the solvent feed. This fluid forms a protective pad 6 at the roof of the cavity. The protective non-solvent fluids tends to flow into the high spots of the cavity insulating these areas from further extraction. In this fashion, horizontal development of a low height cavity is encouraged. Once communication is attained, development of the cavity roof up into the product mineral deposit is encouraged by decreasing the amount of protective fluid at the cavity roof. It is normally desirable that the roof rise into the product minerals along substantially the entire cavity roof area.

Without limiting the invention in any way, it can be pointed out that it is particularly applicable to solution mining KCl-rich. NaCl deposits of the type locatedin Saskatchewan, Canada. These deposits are located several thousand feet beneath the surface of the earth and comprise a plurality of strata of widely varying composition. Beneath the KCI-rich strata there is a substantial bed of material which contains essentially no KCl, being substantially wholly NaCl. Within the KCI-rich deposit, the KCI concentration varies widely and is interrupted by zones or strata which contain little, i.e., less than about 15 percent by weight KCl, basis the total weight of NaCl and KCl on the deposit. The entire formation contains a plurality of insoluble seams notably of clay and calcium sulfate. A large extraction surface is particularly desirous in solution mining KCl deposits because of the substantial negative heatof solution of .KCl. Thus, in the Saskatchewan deposits, the instant invention is particularly advantageous. A flexible conduit such as a hose, flexible pipe, slotted pipe or jointed pipe is provided through the deposit to an insoluble calcium sulfate band located in the upper region of the NaCl rich deposit and directly beneath a KCl-rich stratum. Communication is effected between two cased bore holes as hereinbefore described.

In this fashion, a large extraction surface is provided ad- I rality of cased bore holes is disposed to communicate with said deposit, a cavity is developed to communicate with an influent bore hole and an efliuent bore hole and.

minerals are extracted from the product stratum by feeding solvent to the cavity through the influent bore hole and withdrawing dissolved product minerals from the cavity through the eflluent bore hole, the improvement which comprises selecting a thin insoluble band located in said deposit in the vicinity of the bottom of said product stratum but above non-product minerals and establishing communication between said bore holes in the vicinity of said thin insoluble band while avoiding extraction of extractable non-product minerals located in the deposit below said thin insoluble band by providing a bore hole to the vicinity of and above said thin insoluble band, providing a second bore hole removed from the first named bore hole and communicating with the vicinity of the insoluble band, providing a flexible conduit through one of said bore holes to contact said insoluble band, biasing said flexible conduit in the direction of the second bore hole and urging the conduit along the upper surface of the insoluble band in the direction of the second bore hole while feeding solvent through said flexible conduit to extract soluble material disposed above the insoluble band and withdrawing effluent through the first bore hole thereby developing a passageway in the direction of the second bore hole until communication is effected between the two bore holes.

2. The method of claim 1 wherein the thin insoluble band is adjacent product minerals.

3. In the solution mining of a KCl-rich stratum located in a deposit rich in NaCl said deposit including substantial amounts of KCl-lean NaCl beneath said KCl-rich stratum and thin bands of insoluble material traversing said deposit, the improvement which comprises selecting a said thin insoluble band in the vicinity of the bottom of said KCl-rich stratum but above KCl-lean NaCl, providing spaced bore holes in communication with the deposit in the vicinity of said selected insoluble band, said establishing communication between said bore holes in the vicinity of said KCl-rich stratum while avoiding extraction of KCl-lean NaCl located in the deposit beneath said thin insoluble band by introducing a flexible conduit down a first bore hole, biasing said flexible conduit in the direction of a second bore hole, introducing extractant down said flexible conduit to extract soluble materials above said insoluble band and removing extracted materials through said first named bore hole while urging the flexible conduit along the upper surface of the insoluble band in the direction of the second bore hole until communication is established between said first and second bore holes.

4. A method of claim 3 wherein the deposit comprises a KCl-rich stratum located between KCl-lean, NaCl-rich strata and the thin insoluble band is located in the NaClrich, KCl-lean stratum beneath the KCl-rich stratum.

5. A method of claim 4 wherein the thin insoluble band is a band of calcium sulfate, consolidated clay, shale, slate or limestone.

References Cited UNITED STATES PATENTS 2,251,916 8/1941 Cross 2995 2,345,816 4/1944 Hays 61.5 X 2,796,129 6/1957 Brandon 166-50 X 2,822,158 2/1958 Brinton 2994 ERNEST R. PURSER, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,347,595 October 17, 1967 James Bowen Dahms et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 6, line 3, for "said", second occurrence, read and Signed and sealed this 5th day of November 1968.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

1. IN THE SOLUTION MINING OF A PRODUCT STRATUM LOCATED IN A SOLUBLE DEPOSIT WHICH INCLUDES STRATE OF VARYING COMPOSITIONS INCLUDING STRATA OF SOLUBLE NON-PRODUCT MINERALS BENEATH SAID PRODUCT STRATUM AND RELATIVELY THIN BANDS OF INSOLUBLE MATERIAL TRAVERSING SAID DEPOSIT WHEREIN A PLURALITY OF CASED BORE HOLES IS DISPOSED TO COMMUNICATE WITH SAID DEPOSIT, A CAVITY IS DEVELOPED TO COMMUNICATE WITH AN INFLUENT BORE HOLE AND AN EFFLUENT BORE HOLE AND MINERALS ARE EXRACTED FROM THE PRODUCT STRATUM BY FEEDING SOLVENT TO THE CAVITY THROUGH THE INFLUENT BORE HOLE AND WITHDRAWING DISSOLVED PRODUCT MINERALS FROM THE CAVITY THROUGH THE EFFLUENT BORE HOLE, THE IMPROVEMENT WHICH COMPRISES SELECTING A THIN INSOLUBLE BAND LOCATED IN SAID DEPOSIT IN THE VICINITY OF THE BOTTOM OF SAID PRODUCT STRATUM BUT ABOVE NON-PRODUCT MINERALS AND ESTABLISHING COMMUNICATION BETWEEN SAID BORE HOLES IN THE VICINITY OF SAID THIN INSOLUBLE BAND WHILE AVOIDING EXTRACTION OF EXTRACTABLE NON-PRODUCT MINERALS LOCATED IN THE DEPOSIT BELOW SAID THIN INSOLUBLE BAND BY PROVIDING A BORE HOLE TO THE VICINITY OF AND ABOVE SAID THIN INSOLUBLE BAND, PROVIDING A SECOND BORE HOLD REMOVED FROM THE FIRST NAMED BORE HOLE AND COMMUNICATING WITH THE VICINITY OF THE INSOLUBLE BAND, PROVIDING A FLEXIBLE CONDUIT THROUGH ONE OF SAID BORE HOLES TO CONTACT SAID INSOLUBLE BAND, BIASING SAID FLEXIBLE CONDUIT IN THE DIRECTION OF THE SECOND BORE HOLE AND URGING THE CONDUIT ALONG THE UPPER SURFACE OF THE INSOLUBLE BAND IN THE DIRECTION OF THE SECOND BORE HOLE WHILE FEEDING SOLVENT THROUGH SAID FLEXIBLE CONDUIT TO EXTRACT SOLUBLE MATERIAL DISPOSED ABOVE THE INSOLUBLE BAND AND WITHDRAWING EFFLUENT THROUGH THE FIRST BORE HOLE THEREBY DEVELOPING A PASSAGEWAY IN THE DIRECTION OF THE SECOND BORE HOLE UNTIL COMMUNICATION IS EFFECTED BETWEEN THE TWO BORE HOLES. 